Barnett Julian, Wirth Konstantin G, Hentrich Richard, Durmaz Yasin C, Rose Marc-André, Gunkel Felix, Taubner Thomas
I. Institute of Physics (IA), RWTH Aachen University, Aachen, Germany.
attocube systems GmbH, Haar, Germany.
Nat Commun. 2025 May 13;16(1):4417. doi: 10.1038/s41467-025-59633-1.
Confined electron systems, such as 2D electron gases (2DEGs), 2D materials, or topological insulators, show great technological promise but their susceptibility to defects often results in nanoscale inhomogeneities with unclear origins. Scattering-type scanning near-field optical microscopy (s-SNOM) is useful to investigate buried confined electron systems non-destructively with nanoscale resolution, however, a clear separation of carrier concentration and mobility was so far impossible in s-SNOM. Here, we predict a previously inaccessible characteristic "fingerprint" response of the prototypical LaAlO/SrTiO 2DEG, and verify it using a state-of-the-art tunable narrow-band laser in mid-infrared cryo-s-SNOM at 8 K. Our modeling allows us to separate the influence of carrier concentration and mobility on fingerprint spectra and to characterize 2DEG inhomogeneities on the nanoscale. Finally, we model the surface accumulation layer in doped InAs, to show that our fingerprint spectra are a universal feature and generally applicable to confined electron systems, like topological insulators or stacked van-der-Waals materials.
受限电子系统，如二维电子气（2DEG）、二维材料或拓扑绝缘体，展现出巨大的技术潜力，但它们对缺陷的敏感性常常导致具有不明起源的纳米级不均匀性。散射型扫描近场光学显微镜（s-SNOM）有助于以纳米级分辨率无损地研究深埋的受限电子系统，然而，到目前为止，在s-SNOM中还无法清晰区分载流子浓度和迁移率。在此，我们预测了典型的LaAlO/SrTiO₂二维电子气此前无法获得的特征“指纹”响应，并在8K的中红外低温s-SNOM中使用最先进的可调谐窄带激光器对其进行了验证。我们的建模使我们能够区分载流子浓度和迁移率对指纹光谱的影响，并在纳米尺度上表征二维电子气的不均匀性。最后，我们对掺杂InAs中的表面积累层进行建模，以表明我们的指纹光谱是一种普遍特征，通常适用于受限电子系统，如拓扑绝缘体或堆叠的范德华材料。
